moon98¶
- erfa.moon98(date1, date2)[source]¶
Approximate geocentric position and velocity of the Moon.
- Parameters:
- date1double array
- date2double array
- Returns:
- pvdouble array
Notes
Wraps ERFA function
eraMoon98
. The ERFA documentation is:- - - - - - - - - - e r a M o o n 9 8 - - - - - - - - - - Approximate geocentric position and velocity of the Moon. n.b. Not IAU-endorsed and without canonical status. Given: date1 double TT date part A (Notes 1,4) date2 double TT date part B (Notes 1,4) Returned: pv double[2][3] Moon p,v, GCRS (au, au/d, Note 5) Notes: 1) The TT date date1+date2 is a Julian Date, apportioned in any convenient way between the two arguments. For example, JD(TT)=2450123.7 could be expressed in any of these ways, among others: date1 date2 2450123.7 0.0 (JD method) 2451545.0 -1421.3 (J2000 method) 2400000.5 50123.2 (MJD method) 2450123.5 0.2 (date & time method) The JD method is the most natural and convenient to use in cases where the loss of several decimal digits of resolution is acceptable. The J2000 method is best matched to the way the argument is handled internally and will deliver the optimum resolution. The MJD method and the date & time methods are both good compromises between resolution and convenience. The limited accuracy of the present algorithm is such that any of the methods is satisfactory. 2) This function is a full implementation of the algorithm published by Meeus (see reference) except that the light-time correction to the Moon's mean longitude has been omitted. 3) Comparisons with ELP/MPP02 over the interval 1950-2100 gave RMS errors of 2.9 arcsec in geocentric direction, 6.1 km in position and 36 mm/s in velocity. The worst case errors were 18.3 arcsec in geocentric direction, 31.7 km in position and 172 mm/s in velocity. 4) The original algorithm is expressed in terms of "dynamical time", which can either be TDB or TT without any significant change in accuracy. UT cannot be used without incurring significant errors (30 arcsec in the present era) due to the Moon's 0.5 arcsec/sec movement. 5) The result is with respect to the GCRS (the same as J2000.0 mean equator and equinox to within 23 mas). 6) Velocity is obtained by a complete analytical differentiation of the Meeus model. 7) The Meeus algorithm generates position and velocity in mean ecliptic coordinates of date, which the present function then rotates into GCRS. Because the ecliptic system is precessing, there is a coupling between this spin (about 1.4 degrees per century) and the Moon position that produces a small velocity contribution. In the present function this effect is neglected as it corresponds to a maximum difference of less than 3 mm/s and increases the RMS error by only 0.4%. References: Meeus, J., Astronomical Algorithms, 2nd edition, Willmann-Bell, 1998, p337. Simon, J.L., Bretagnon, P., Chapront, J., Chapront-Touze, M., Francou, G. & Laskar, J., Astron.Astrophys., 1994, 282, 663 Defined in erfam.h: ERFA_DAU astronomical unit (m) ERFA_DJC days per Julian century ERFA_DJ00 reference epoch (J2000.0), Julian Date ERFA_DD2R degrees to radians Called: eraS2pv spherical coordinates to pv-vector eraPfw06 bias-precession F-W angles, IAU 2006 eraIr initialize r-matrix to identity eraRz rotate around Z-axis eraRx rotate around X-axis eraRxpv product of r-matrix and pv-vector This revision: 2023 March 20 Copyright (C) 2013-2023, NumFOCUS Foundation. Derived, with permission, from the SOFA library. See notes at end of file.